Free gas entering the pump is one of the most common reasons production falls short of design. Gas interference is not the same as fluid pound and not the same as gas lock, and the fix for each is different. Getting the diagnosis right is what separates a productive intervention from an expensive one that does not help.
Three Conditions, One Source
Gas interference: free gas enters the pump with liquid. The barrel fills partially. Valve action gets soft and rounded because the gas compresses and expands instead of producing sharp pressure changes. Production continues but below design.
Gas lock: gas becomes trapped between the traveling valve and standing valve. It compresses on the downstroke but does not generate enough pressure to open the traveling valve. Both valves stay closed. Production drops to near zero.
Fluid pound: the well is pumped off. The barrel has little liquid to fill with, the plunger slams into what liquid there is, and the shock loads accelerate mechanical failures. Different root cause entirely - the reservoir cannot supply the pump.
Reading the Cards
Gas interference: rounded, elongated, banana-shaped downhole card. Load builds gradually instead of picking up sharply. Fillage below 30 to 50 percent. Surface card shows reduced area and softer transitions.
Gas lock: flat or near-flat card because neither valve is opening. Very low dynamic load variation. The pump is running but moving no fluid.
Fluid pound: rectangular card with a sharp drop near top of the downstroke where the plunger strikes liquid. Fluid level shots show low submergence. The distinction from gas interference is critical - if fluid level is high and fillage is low, the problem is gas, not pumped-off.
Why Gas Gets In
The pump intake is above a gas-rich zone of the fluid column. Gas separators are undersized or absent. The well has a high gas-oil ratio and continuous gas evolution from the flowing fluid. The pump is set too shallow relative to perforations so gas in the casing enters through the intake before it can separate.
The Fixes in Order
Downhole gas separators (poor-boys, packer-type, or Echometer-tested designs) separate gas from liquid before the intake. Set the pump as deep as possible below the perforations to allow natural gas separation in the annulus. Lower SPM to give the barrel more time to fill and gas more time to separate. Compression ratios on the pump matter - a higher compression pump handles more free gas before locking.
When interference is chronic and mechanical fixes reach their limit, a different artificial lift method may be justified. ESPs, gas lift, and progressing cavity pumps each have different gas tolerance envelopes. Rod pumps can handle modest gas fractions well. Severe continuous gas is where other methods start to win.
Bottom Line
Gas interference is distinguishable from gas lock and fluid pound on the card and the fluid level shot. Solving it starts with the pump intake geometry and gas separation design, not with the pump itself. Getting these right typically recovers 10 to 30 percent production on high-GOR wells.